Arterial calcification commonly develops in association with atherosclerosis, aging, diabetes mellitus (DM), and renal failure and contributes to excess cardiovascular mortality and morbidity. In atherosclerosis, lesion intimal calcification is directly associated with leukocyte-mediated inflammation and modulated by oxidant stress via products of lipoprotein oxidation. In contrast, artery tunica media calcification may be more widely spread through the arterial tree, reflecting systemic changes in mediators of calcification. But common to both forms of artery calcification is altered differentiation of lesional cells, manifested by an active process with features resembling skeletal endochondral bone formation. Recently, we linked human "idiopathic" infantile arterial calcification (IIAC) to deficiency of NPP1, which generates the physiologic calcification inhibitor PPi. IIAC is a spontaneous form of widely disseminated large artery media calcification and is commonly associated with periarticular calcifications, similar to findings in NPPl-deficient mice. Preliminary studies reveal chondroid metaplasia within aortic cells in situ and enhanced calcification by enriched (>95% a-actin positive) VSMCs from aortas of two mice with extracellular PPi depletion and remarkably similar pathologic skeletal calcification (i.e., NPP1 null mice and ank/ank mice in which the PPi channelling function of ANK is disabled). We will test the hypothesis that extracellular PPi depletion promotes artery calcification by a 2-step process of chondrogenesis, and chondrocytic maturation to hypertrophy in VSMCs and pluripotential cells in arteries, mediated by selective PPi-mediated changes in expression of the oxidant stress regulator vanin-1 -pantetheinase and by the inflammatory pro-atherogenic chemokine KC/GROa (CXCL1), respectively. Completion of these studies will link alterations in VSMC PPi metabolism with modulation of oxidant stress and chemokine responses pertinent to pathologic calcification in both degenerative disorders and atherosclerosis. [unreadable] [unreadable]